30 I C O N T R A I L S I S P R I N G 2 0 1 4S P R I N G 2 0 1 4 I C O N T R A I L S I 31

The world is a very different place from 43,000 feet. It may be only 2,000 feet

above the more normal FL410, but it’s an impressive height for a Citation 500.

Of course, the airplane that has me surrounded today isn’t your rich uncle’s

first-generation Citation. It’s a Sierra Industries Eagle II conversion, with Williams

FJ44-2A engines in place of the standard Pratt &Whitney JT15Ds.

As I look down on the Grand Canyon slicing off the top of Ar-

izona eight-and-a-half miles below, I can see Monument Valley

to the east and Lake Mead to the west. Cowboy country unfolds

below me as we transition north into Utah, and the Citation’s TAS hovers right

at 350 knots, about 40 knots quicker than it has any right to be at this altitude.

OK, I can’t see the Earth’s curvature from this height, but I’m cruising well above

many other corporate jets and virtually all airliners, and I’m doing so at a speed

any Citation 500/501 owner would envy.

sierra industries

CESSNA EAGLE II CONVERSIONMANUFACTURERS DON’ T ALWAYS GET IT RIGHT, STRAIGHT OUT OF THE BOX. By Bill Cox

MODSQUAD

32 I C O N T R A I L S I S P R I N G 2 0 1 4S P R I N G 2 0 1 4 I C O N T R A I L S I 33

“My” Eagle for the day is a demonstrator with most of the bells and whistles you can put on it. The airplane is almost antithetical to the traditional image of a business jet. It’s ridiculously simple to fly, with uncomplicated though not-quite-FADEC engine controls, a low landing ref speed, benign stall characteris-tics, improved short-field performance, gentle handling and an uncomplicated panel layout. Such a forgiving configuration and flight manners are practically generic to Citations, but the Eagle II conversion also emphasizes performance and efficiency. Since 1983, when

Mark Huffstutler and his father started the company in Uvalde, Texas, Sierra’s mission has been to make a variety of early Cita-tions fly faster and more efficiently. They’ve acquired or created some 300 STC’d products over the last 30 years, everything from Robertson STOL and Dee Howard to Astec and Branson in addition to their own mods. Today, Sierra holds more aviation STCs than any other company in America. By far, Sierra’s most comprehensive product is the Eagle II conversion for the Citation 500 and 501. Huffstutler explains the rationale

of modifying those first Citation 500s and 501s. “The airplane is a modifier’s dream. The beauty of the Citation is that Cessna didn’t go to great lengths to tweak the airplane for max performance. They just wanted a cheap, easy jet (to fly). There’s a lot of room for improve-ment — paradise for a modifier.” In its final production configuration, the basic Citation was a huge gamble for Cessna. The company spent $35 million on development and certification of its en-try-level jet, and you have to remember, this was the late ‘60s. In those days, $35 million

was “real money,” about half the company’s net worth. Up until then, Cessna’s products were almost exclusively piston-powered. Even the Conquest l and ll turboprops were still years away. If the Citation hadn’t caught on, Cessna could very well have folded. At the time, the Lear was the jet of choice, the sexiest non-military aircraft in the sky. In 1972, Cessna offered the first production Citation 500 for $625,000. In contrast, the comparable Lear 24 was listed at a base $854,000, nearly a quarter million dollars more expensive, but also possessing much improved performance. Contrary to popular belief, the Citation 500 wasn’t Cessna’s first jet. In fact, the orig-inal Citation wasn’t even its own airplane. It sprang from the company’s T-37 USAF trainer, nicknamed the Tweet because of its Continental jet engines’ high-pitched scream. The T-37 was the rough template for the company’s planned first corporate jet, the model 407, a four-seater with a proposed 400-knot cruise and a ceiling of 46,000 feet. That concept never left the drawing boards, partly because Cessna wasn’t sure there was a market for a four-seat business jet. In retrospect, it may have been right. To that end, Cessna’s originally named Fanjet 500 (changed to Citation 500 before produc-tion began) was an eight-seat, 350-knot mod-el that finally premiered in 1972. The airplane has evolved through more than a dozen iterations since then, offering significantly more power, cruise performance approach-ing Mach 1.0, stretched cabins and half a rain forest of mahogany. For those critics who laughed at the original airplane’s bulbous nose and high dihedral, cruciform tail, Cess-na can now lay claim to having built roughly a third of all the business jets on or above the planet. Better still, from Sierra’s point of view, the available matrix of 500s/501s is huge. Hundreds of the original 500/501s are still available on the used market. Sierra Industries begins the conversion process by removing the P&W JT15Ds and installing a pair of Williams FJ44-2A turbo-fans. Among the 689 early Citations produced, Sierra estimates some 450 are eligible for their power-up. The rest are already approved to FL410, and the performance improvement wouldn’t be as significant on those models. The immediate result of the engine swap is a significant sea-level thrust increase that generates a major climb improvement. The original Citation 500 could manage about 2,700 fpm climb with a full load, adequate but not spectacular. After the conversion

to the Williams engines, the airplane ascends at more like 4,500 fpm, and the FJ-44 turbines deliver 35 percent more thrust than the Pratts at 41,000 feet. Better still, the stock 500 required about 80 minutes to step climb up to 41,000 feet, whereas the Eagle II levels at 43,000 feet in about 25 minutes. The higher thrust level above 41,000 feet also helps boost max cruise to about 390 knots, again roughly 40 knots better than the best efforts of the 500 and 501. Sierra sells the engine conversion by itself as the Stallion, but the full Eagle II is by far the more popular mod. Between the two models, Sierra has sold 50 of the basic Citation conversions. The Eagle II includes a major change to the inboard wing, specifically, the airfoil between the root and midspan. In flow-test-ing the original wing, engineers discovered that section was suffering a major drag rise during climb or any other high angle-of-at-tack attitude. This, in turn, was partially inhibiting airflow through the aft-mounted engines and reducing available thrust. As a result, the inboard airfoil was reshaped to provide more laminar flow and better thrust recovery. This produced a no-table hump in the inboard wing section, and Sierra uses that additional space to increase fuel capacity from the 3,600 to 4,510 pounds. The extra fuel obviously has a major effect on range, and in combination with the high-er thrust rating, allows the airplane to cover 1,650 nm between pit stops. That makes one stop, coast-to-coast trips possible in a single, fairly easy day. Considering that you can travel on your own schedule in first-class comfort and be assured that your bags will arrive at the same time you do (and at no extra cost), that’s a major consideration. While dealing with the wings, Sierra in-creases span by 19 inches a side, roughly the same as on the Citation 501. According to Huffstutler, the bottom line for Eagle II own-ers is not only better climb, speed, service ceiling and range but improved efficiency. At high cruise altitudes, the airplane delivers 35 percent more thrust on 40 percent less fuel. He explained the improved fuel burn: “On the old airplanes, at top of climb, you’d see about .30 nautical miles per pound of fuel burned. At the top of descent at a lightweight, you’d see .35 to .38. The Eagle II levels off at .50 and … goes to .60 or better, equivalent to a CJ-2.” Considering that you can purchase a decent Citation 500 or 501 for as little as

$300,000, the Eagle II conversion price of approximately $1.950 million seems relatively inexpensive. The price is only approximate, because Sierra will

allow a trade-in value on your existing Pratt and Whitney JT15D engines, de-

pending upon time and condition. Sierra also sells a variety of other up-grades, from a full glass panel, to a custom leather interior and new paint. That means if you don’t change paint or avionics, you could be back in the sky with a near 400 knot, eight-seat jet for less than $2.5 million. In contrast to new prices, nothing even comes close to the same performance at the same price point. It’s tough to compare any used jet to a new-generation CJ-2 with a full-glass panel and the latest avionics, but the new Citation model sells for $7.3 million. In fact, however, the depressed market for legacy Citations has minimized de-mand, encouraging folks with an interest in the Eagle II to search the used market for already-converted airplanes rather than purchase an original 500/501 and convert it. This avoids the long downtime associated with the structural wing mods and instal-lation of the additional 900-pound fuel op-tion. Those pilots interested in minimizing time constraints might consider the Stallion conversion, which swaps engines without the other mods. For that reason, the Stallion and Eagle II aren’t Huffstutler’s only conversions. Sierra offers a mod on the stretched Citation II (technically known as the model 550) called the Super II. This replaces the P&W JT15D-4 turbine mills with the more power-ful, Williams FJ44-3A engines for the same price as the Eagle mod. As with the Eagle II STC, this adds 2,000 feet to service ceiling, plus a 25 percent in-crease in range and about 30 knots to cruise. There’s also an optional aft-cabin fuel tank that boosts fuel capacity by 900 pounds and a gross weight increase of as much as 1,200 pounds, depending upon serial number. So far, Sierra has converted 12 Citation IIs to what they call the Super II configuration. When you compare price, performance and operating costs of the Sierra conversions to more modern Citations, you can’t avoid the conclusion that an STC’d model will probably cost you less than 50 percent of the price of a new airplane with comparable performance. Whatever your perspective on cost, Sierra’s Stallion, Eagle II and Super II con-versions of the early Citations provide an interesting alternative to buying new.

sierra industries

Since 1983, when Mark Huffstutler and his father started the company in Uvalde, Texas, Sierra’s mission has been to make a variety of early Citations fly faster and more efficiently.

MODSQUAD